[alex_lav]

> how should I demonstrate skills?

Your list is correct. Any/all. Open source everything and if you make a game engine, make games in it.

> is engine programming less exploitative?

Depends on how you mean. Working in the games industry usually involves dealing with the same handful of warts regardless of where you go and what your title is. The exception is depending on your seniority/role/specialization, those warts may manifest differently. As a junior engine programmer, you're still going to have to deal with the same things any lower ranking games industry person is going to have to deal with.

With time though, engine programmer becomes one of those specs where the money is insane and the job security is better than usual.